1. Field of the Invention
The present invention relates to an outer appearance quality inspection system for electronically and optically detecting and judging the outer appearance and grades such as size, stain or visible damages and color of objects such as fruits and sorting them according to their sizes and grades. The outer appearance quality inspection system in accordance with the present invention is preferably adaptable for use in automatic sorting of oranges.
2. Description of the Prior Art
So far sieves or screens have been commonly used in order to classify oranges according to their sizes. When such sieve or screen classification system is employed, the oranges must be conveyed for a long distance. As a result, the oranges collide with each other and with other members of the system and are caused to rotate many times. In addition, they fall through the sieve for a long distance. As a consequence, they are likely to be damaged.
In order to classify the oranges according to their color and visible damages, people in charge of such classification must handle each orange, but the classification standards are different among those people. That is, their classification standards are varied. Furthermore, such manual classification is cumbersome and not efficient.
There has been devised an automated orange sorting system with photoelectronic conversion devices, but its use is limited only to one function such as the detection of size, color or visible damage of oranges. Furthermore, the automatic orange sorting system is very complicated in construction. Moreover, the classification results are not satisfactory, because the system cannot perform exact sorting of the oranges according to their size, color or visible damages. Thus, the automatic orange sorting system is not satisfactory in practice.
In the case of classification of oranges according to their sizes, the classification results vary depending upon whether an orange is disposed along the center line of a conveyor belt or offset from the center line. In the automatic orange sorting system, the offset of an orange from the center line of the conveyor is measured in order to obtain a true size of an orange. The size of an orange is defined as the maximum diameter of the equator of the orange which divides the orange into two equal parts, i.e., top and bottom parts.
In the prior art automatic orange sorting system, optoelectronic switches are used to measure the size of oranges. Only one pair of optoelectronic switches may sufficiently be used if an orange is transported by a conveyor belt with its top or bottom portion directed upwardly, but when an orange is transported by a conveyor in such a way that its equator is positioned vertically, a large number of optoelectronic switches must be disposed vertically. The accuracy of measurement of the size of an orange is dependent upon the distance between the vertically spaced optoelectronic switches, so that it is difficult to accurately measure the size of an orange. Furthermore, the automatic orange sorting system is complicated in construction.
In order to detect the color of an orange, the green light (G) and the red light (R) which are very sensitive to the color change of the orange and the infrared ray (IR) which is not so sensitive to the color change of the orange are directed to the same spot on the surface of the orange. The reflected light rays from the spot are sensed in order to compute ratios IR/R and IR/G between the levels G, R and IR of the reflected green and red light rays and infrared ray. The color of the orange is detected from such ratios. However, such system as described above has a complicated arrangement and there has not been available yet a means for displaying the computed ratios in a suitable manner for inspection.
The classification of oranges in accordance with their visible damages has been difficult and has the following problems. First, when an orange which is being transported by a conveyor belt is viewed from its one side, the peripheral portion of the orange is viewed to be dark because the oranges are in general in the form of sphere. As a result, the dark portion is erroneously detected as a visible damage. Secondly, a TV camera output in response to the light reflected from the green portion of an orange is low, so that it is difficult to detect visible damages on the green portion. Thirdly, the TV camera output in response to visible white or silver white damages is almost the same as the output in response to the light reflected from other portions of an orange. Fourthly, the portions such as small projections like bubbles of white-yellow color which have a high reflectivity are erroneously detected as visible damages. Fifthly, since oranges are in general in the form of a sphere, there always exists a point at which the angle of incidence and the angle of reflection are equal to each other. Therefore, it follows that if a visible damage exists at such a point, it cannot be detected.